Satellites in orbit encounter quite large temperature variations depending of their exposure to the solar energy. However, their internal temperature should be controlled to an optimal operating temperature range in order to keep all the electronic systems function under stabilized conditions.
Radiators are usually used for maintaining the internal temperature of a satellite within the optimal operating temperature range. The heat exchange between the radiator and its environment is mainly controlled through radiation, which is in turn determined by the radiator emittance. Therefore, the thermal control of the satellite internal temperature may be achieved via the use of a radiator having variable emittance surfaces. By adapting the emittance value to the external temperature, it is possible to radiate more or less heat so that a control of the temperature of the satellite is achieved.
There are mainly two types of radiators used for the thermal control systems of satellites, i.e. active and passive approaches. The active approach includes all the thermal management systems that are activated electrically. One example of an active radiator consists in an active thermal control system comprising electro-mechanical louvers formed of highly reflective metal blades which open and close depending on the external temperature to expose more or less area of an emissive surface. The control of the electro-mechanical louvers requires temperature sensors, power supply and control circuits, which makes them complex, expensive, and/or bulky.
A passive radiator is a passive variable emittance device comprising a coating having an emittance that can self-adjust with the temperature. For example, it has been reported in the prior art that coatings made of lanthanum-strontium-manganate may present a change in the emittance from 0.37 to 0.67 while the temperature increasing from 220K to 340K. However, the maximum emittance at high temperature, i.e. 0.67, may not be sufficient for evacuating heat.
Therefore, there is a need for an improved passive variable emittance device having applications in at least the field of satellites.